I was watching the Niners-Lions game last week and saw something that has me a little confused. I was under the impression that when a quarterback slides in the NFL, the play is considered dead when the player hits the ground. In this video, 49er QB Alex Smith starts sliding and then is hit. I know the timing is really close, but it seems like the defender (safety John Wendling) moved after Smith was already going down. In the instance that a player is hit after the play is dead, I thought there was supposed to be a penalty like unnecessary roughness. I haven't been able to find a rule about QB slides anywhere, except some speculation on it.

First, is the play dead after a QB slides, regardless of whether he is hit? Second, if it is dead on the slide, is there a penalty for hitting the QB after the slide?

When a runner declares himself down by sliding feet first on the
ground. The ball is dead the instant the runner touches the ground
with anything other than his hands or his feet;

Additionally, a note states:

Defenders are required to treat a sliding runner as they would a
runner who is down by contact.

A defender must pull up when a runner begins a feet-first slide. This does not mean that all contact by a defender is illegal. If a defender has already committed himself, and
the contact is unavoidable, it is not a foul unless the defender commits some other act, such as helmet-to-helmet contact or by driving his forearm or shoulder into the head or neck are of the runner.

This is a comment but just too long of one to go in comments. Both other answers are kind of right. This answer has the rule cited but you can look at the rule for 20 seconds and figure out that it is missing a lot of clarity.

The rules committee will certainly address the shortcomings of this rule in the offseason. If you watched the Packers game last night (11/20/16 vs Redskins) you will note that Rodgers went head first twice and both times he was declared to have given himself up. One of the times he got up and tried to run more... what a mess the NFL has gotten themselves into.

Not only is there a large amount of ambiguity on what it means to give oneself up, but there is a no frills circumvention to this rule - slide head first. Nobody can hit you because maybe you did give yourself up and then if they don't hit you, you can get up and start running again. Completely ridiculous. And this is only an NFL problem, as other leagues the knee down is a down play. To make matters worse 80-90% of the slides are by QBs.

So the "correct" answer at this point in time is that there is a rule that clearly states that a player is down at the beginning of their slide when going feet first (the NFL hasn't spotted this right all year and gives QBs 1-2 yards extra per slide). Letter d - addressing feet first sliding - isn't even how it is called in games. The rule says "the instant a runner touches the ground". That is not how NFL referees call it. The runner is down as soon as he starts his slide, which affords him extra protection from being hit. This is unarguable since there are 20 late hits a year that happen far from the runner beginning his slide but close to when the runners body hits the ground.

Now the other side of this is when the QB slides head first. This wasn't meant to be a dead ball, however to keep up with player safety and the horribly vulnerable position a player is in (head facing the defense, laying on the ground), NFL referees have in almost all cases this year declared the player as giving himself up when the QB slides head first (I simply can't remember a non-QB sliding head first that wasn't touched - please comment if there is one).

So Rodgers being the smart QB he is tried to use a loophole to gain protection and then get back up. The referees were smarter than Rodgers in both cases and declared that he declared himself down. To me this is rather interesting because unlike the feet first slide, and to go along with the "down or not" ambiguity, we also have an issue with the spot of the ball.

On a face first slide you are moving forward. If you are talking about the inches of the game and not safety you certainly would want your defensive player cremating Rodgers to physically knock his body backwards. All coaches know that if you pat a sliding player on the back, the referees are more apt to give him a few extra inches (feet) after the touch. If you stop him in his tracks, you might help your cause by a few inches. Then you have the QB with the ability to possibly get up because the rules don't clearly say he is down.

This basically makes the referees make a both strategic and safety decision on every head first slide. I think the NFL will continue to rule to QB down on any slide and amend the rules ASAP. As a coach I could certainly see telling your players... Just hover a couple yards from him after a slide and lay him out if he gets up without a whistle.

If a qb is running he becomes runner and can be hit like any other player. The play is over whether he slides feet or head first.. ( he is giving himself up) any player can give themself up.. no penalties if a defender is in the process

This answer doesn't provide any references, and contradicts another answer. Could you provide some links to official sources to back up your points please?
– TrueDubNov 21 '16 at 13:26

@TrueDub this doesn't really seem to me to contradict the other answer in any of the significant points: they both say that the play is over once a runner begins a slide, and that a defender can hit the sliding player only if they were already committed to the action before the slide started.
– Philip Kendall♦Nov 21 '16 at 15:23

My reading of the first answer is that only a feet-first slide counts as declaring himself down. "Contradicts" is probably too strong a word, but this answer expands the criteria, but without backing it up. I've also noticed how old this question is, thought it was a lot newer.
– TrueDubNov 21 '16 at 15:55

2

@PhilipKendall - I added a long comment/answer. I think you are being a little hard on this person. The NFL referees have basically called it like this all year.
– Coach-DNov 21 '16 at 19:08